A head of government (or head of the executive), known as the prime minister (PM), premier, or first minister. While the head of state appoints the head of government, constitutional convention suggests that a majority of elected Members of Parliament must support the person appointed.[6] If more than half of elected parliamentarians belong to the same political party, then the parliamentary leader of that party typically is appointed.[6] An exception to this was Israel, in which direct prime-ministerial elections were made in 1996, 1999 and 2001.

An executive branch led by the head of government usually made up of members of the legislature with the senior members of the executive in a cabinet adhering to the principle of cabinet collective responsibility; such members execute executive authority on behalf of the nominal or theoretical executive authority.

An independent, non-partisan civil service which advises on, and implements, decisions of those ministers. Civil servants hold permanent appointments and can expect merit-based selection processes and continuity of employment when governments change.[7]

Parliamentary privilege, which allows the legislature to discuss any issue it deems relevant, without fear of consequences stemming from defamatory statements or records thereof

Minutes of meetings, often known as Hansard, including an ability for the legislature to strike discussion from these minutes

The ability of courts to address silence or ambiguity in the parliament's statutory law through the development of common law. Another parallel system of legal principles also exists known as equity though this has mostly been merged with common law or codified into statutory law. Exceptions to this include India, Quebec in Canada, and Scotland in the UK amongst others which mix common law with other legal systems.

However, uncodified conventions, practices, and precedents continue to play a significant role in most countries, as many constitutions do not specify important elements of procedure: for example, some older constitutions using the Westminster system do not mention the existence of the cabinet or the prime minister, because these offices were taken for granted by the authors of these constitutions. Sometimes these conventions, reserve powers, and other influences collide in times of crisis and in such times the weaknesses of the unwritten aspects of the Westminster system, as well as the strengths of the Westminster system's flexibility, are put to the test. As an illustrative example, in the Australian constitutional crises of 1975 the Governor-General of Australia, Sir John Kerr, dismissed Prime Minister Gough Whitlam on his own reserve-power authority and replaced him with opposition leader Malcolm Fraser.

The pattern of executive functions within a Westminster System is quite complex. In essence, the head of state, usually a monarch or president, is a ceremonial figurehead who is the theoretical, nominal or de jure source of executive power within the system. In practice, such a figure does not actively exercise executive powers, even though executive authority may be exercised in their name.

As an example, the Prime Minister and Cabinet (as the de facto executive body in the system) generally must seek the permission of the head of state when carrying out executive functions. If, for instance the British Prime Minister wished to dissolve parliament in order for a general election to take place, the Prime Minister is constitutionally bound to request permission from the sovereign in order to attain such a wish. This power (along with others such as appointing ministers in the government, appointing diplomats, declaring war, and signing treaties, for example) is known as the Royal Prerogative, which in modern times is exercised by the sovereign solely on the advice of the Prime Minister. Since the British sovereign is a constitutional monarch, he or she abides by the advice of his or her ministers, except when executing reserve powers in times of crisis.

The head of state will often hold meetings with the head of government and cabinet, as a means of keeping abreast of governmental policy and as a means of advising, consulting and warning ministers in their actions. Such a practice takes place in the United Kingdom and India. In the UK, the sovereign holds confidential weekly meetings with the Prime Minister to discuss governmental policy and to offer her opinions and advice on issues of the day. In India, the Prime Minister is constitutionally bound to hold regular sessions with the President, in a similar manner to the aforementioned British practice. In essence, the head of state, as the theoretical executive authority, "reigns but does not rule". This phrase means that the head of state's role in government is generally ceremonial and as a result does not directly institute executive powers. The reserve powers of the head of state are sufficient to ensure compliance with some of their wishes. However, the extent of such powers varies from one country to another and is often a matter of controversy.

Such an executive arrangement first emerged in the United Kingdom. Historically, the British sovereign held and directly exercised all executive authority. George I of Great Britain (reigned 1714 to 1727) was the first British monarch to delegate some executive powers to a Prime Minister and a cabinet of the ministers,[citation needed] largely because he was also the monarch of Hanover in Germany and did not speak English fluently. Over time, arrangement continued to exercise executive authority on the sovereign's behalf. Such a concept was reinforced in The English Constitution (1876) by Walter Bagehot, who emphasised the "dignified" and "efficient" aspects of government. In this sense Bagehot was stating that the sovereign should be a focal point for the nation, while the PM and cabinet actually undertook executive decisions.

The head of state or his or her representative (such as a governor-general) formally appoints as the head of government whomever commands the confidence of the elected chamber of the legislature and invites him or her to form a government. In the UK, this is known as kissing hands. Although the dissolution of the legislature and the call for new elections is formally performed by the head of state, the head of state, by convention, acts according to the wishes of the head of government.

A president, monarch, or governor-general might possess clearly significant reserve powers. Examples of the use of such powers include the Australian constitutional crisis of 1975 and the Canadian King-Byng Affair in 1926. The Lascelles Principles were an attempt to create a convention to cover similar situations, but have not been tested in practice. Because of differences in their written constitutions, the formal powers of monarchs, governors-general, and presidents vary greatly from one country to another. However, as sovereigns and governors-general are not elected, and some presidents may not be directly elected by the people, they are often shielded from any public disapproval stemming from unilateral or controversial use of their powers.

In the book The English Constitution, Walter Bagehot emphasised the divide of the constitution into two components, the Dignified (that part which is symbolic) and the Efficient (the way things actually work and get done), and called the Efficient "Cabinet Government".[8] Although there have been many works since emphasising different aspects of the "Efficient", no one has seriously questioned Bagehot's premise that the divide exists in the Westminster system, though Israel and Japan operates without the "Dignified" part of government.

Members of the Cabinet are collectively seen as responsible for government policy, a policy termed cabinet collective responsibility. All Cabinet decisions are made by consensus, a vote is rarely taken in a Cabinet meeting. All ministers, whether senior and in the Cabinet, or junior ministers, must support the policy of the government publicly regardless of any private reservations. When a Cabinet reshuffle is imminent, a lot of time is taken up in the conversations of politicians and in the news media, speculating on who will, or will not, be moved in and out of the Cabinet by the Prime Minister, because the appointment of ministers to the Cabinet, and threat of dismissal from the Cabinet, is the single most powerful constitutional power which a Prime Minister has in the political control of the Government in the Westminster system.

In a Westminster system, some members of parliament are elected by popular vote, while others are appointed. Nearly all Westminster-based parliaments have a lower house with powers based on those of the House of Commons (under various names), comprising local, elected representatives of the people (with the only exception being elected entirely by Nationwide PR). Most also have a smaller upper house, which is made up of members chosen by various methods:

Termless appointees, either lifetime or retiring, from successive Prime Ministers (such as the Canadian Senate)

Appointees of the premier and the opposition leader (such as the Jamaican Senate)

In the UK, the lower house is the de facto legislative body, while the upper house practices restraint in exercising its constitutional powers and serves as a consultative body. In other Westminster countries, however, the upper house can sometimes exercise considerable power.

Australia is, in many respects, a unique hybrid with influences from the United States Constitution as well as from the traditions and conventions of the Westminster system. Australia is exceptional because the government faces a fully elected upper house, the Senate, which must be willing to pass its budgets. Although government is formed in the lower house, the House of Representatives, the support of the Senate is necessary in order to govern. The Senate maintains the ability similar to that held by the British House of Lords, prior to the enactment of the Parliament Act 1911, to block supply against the government of the day. A government that is unable to obtain supply can be dismissed by the Governor-General: however, this is generally considered a last resort and is a highly controversial decision to take, given the conflict between the traditional concept of confidence as derived from the lower house and the ability of the Senate to block supply. Many political scientists have held that the Australian system of government was consciously devised as a blend or hybrid of the Westminster and the United States systems of government, especially since the Australian Senate is a powerful upper house like the U.S. Senate; this notion is expressed in the nickname "the Washminster mutation".[9] The ability of upper houses to block supply also features in the parliaments of most Australian states.

Hong Kong, a former British crown colony and currently a special administrative region of the People's Republic of China, has a unicameral Legislative Council. While the Legislative Councils in British Australasian and North American colonies were unelected upper houses and some of them had since abolished themselves, the Legislative Council of Hong Kong has remained the sole chamber and had in 1995 evolved into a fully elected house, yet only part of the seats are returned by universal suffrage. Responsible government was never granted during British colonial rule, and the Governor remained the head of government until the transfer of sovereignty in 1997, when the role was replaced by the Chief Executive. Secretaries had remained to be chosen by the Chief Executive not from the Legislative Council, and their appointments need not be approved by the Legislative Council. Although essentially more presidential than parliamentary, the Legislative Council had inherited many elements of the Westminster system, including parliamentary powers, privileges and immunity, and the right to conduct inquiries, amongst others. Minutes are known as Hansards, and the theme colour of the meeting chamber is red as in other upper houses. Government secretaries and other officials are seated on the right hand side of the President in the chamber. The Chief Executive may dissolve the Legislative Council under certain conditions, and is obliged to resign, e.g., when a re-elected Legislative Council passes again a bill that he or she had refused to sign promulgate.

Cabinet members do not have much independence to actively disagree with government policy, even for productive reasons. A cabinet member may be forced to resign simply for opposing one aspect of a government's agenda, even though they agreed with the majority of other proposals. Westminster cabinets also have a tendency to be very large. As the cabinet is the chief organ of power and influence in the government, members of parliament may actively lobby for a position in cabinet once their party is elected to power. The Prime Minister, who is also party leader, will have an active interest in promoting as many of these members from their own party as possible.

Westminster governments usually do not have a very strong tradition of separation of powers, in practice (apart from the separation between the executive/legislature and the judiciary). Though the head of state, be it governor-general, monarch, or president, will have nominal powers to "check" those of the prime minister, in practice these individuals are usually regarded as little more than figureheads who are expected not to actively intervene in day-to-day politics. Prime ministers under any Westminster system have ample freedom to appoint a large variety of individuals, such as judges, cabinet ministers, and other senior bureaucrats.

Nevertheless, prime ministers can usually do only as much as public opinion and the balance of party membership of parliament will let them do. In practice, government in multi-party consociational systems, such as Belgium or the Netherlands, is always made up of coalitions, and prime ministers must keep the coalition partners happy in order to retain their support on votes of confidence. By contrast, in countries with a strong two-party system, such as the United Kingdom and Australia, coalitions rarely occur except when a third party wins an unusually large number of parliamentary seats, or in times of national crisis, when all parties may be represented in the government in order to promote national unity.

The threat posed by non-confidence votes is often used to justify extremely well-disciplined legislative parties in Westminster systems. In order to ensure the government always has the confidence of the majority of the house, the political culture of Westminster nations often makes it highly unusual for a legislator to vote against their party. Critics argue this in turn undermines the freedom and importance of Members of Parliament (MPs) in day-to-day legislating, making the cabinet the only organ of government where individual legislators can aspire to influence the decisions of the government.

Most senior policy will be made at the cabinet level, regardless of what individual MPs may or may not decide in committee, thus reducing the strength of committees. Their greatest power is often the ability to force a government to reveal certain pieces of information.

The Westminster system has a very distinct appearance when functioning, with many British customs incorporated into day-to-day government function. A Westminster-style parliament is usually a long, rectangular room, with two rows of seats and desks on either side. The chairs are positioned so that the two rows are facing each other. This arrangement is said to have derived from an early Parliament which was held in a churchchoir. Traditionally, the opposition parties will sit in one row of seats, and the government party will sit in the other. Of course, sometimes a majority government is so large that it must use the "opposition" seats as well. In the lower house at Westminster (the House of Commons) there are lines on the floor in front of the government and opposition benches that members may cross only when exiting the chamber. It is often rumoured that the distance between the lines is that of the length of two swords although no documentary evidence exists to support this and, in fact, weapons have never been allowed in the Palace of Westminster at any time.

At one end of the room sits a large chair, for the Speaker of the House. The speaker usually wears a black robe, and in many countries, a wig. Robed parliamentary clerks often sit at narrow tables between the two rows of seats, as well.

Other ceremonies sometimes associated with the Westminster system include an annual Speech from the Throne (or equivalent) in which the Head of State gives a special address (written by the government) to parliament about what kind of policies to expect in the coming year, and lengthy State Opening of Parliament ceremonies that often involve the presentation of a large ceremonial mace.

The Westminster system was adopted by a number of countries which subsequently evolved or reformed their system of government departing from the original model. In some cases, certain aspects of the Westminster system were retained or codified in their constitutions. For instance South Africa and Botswana, unlike Commonwealth realms or parliamentary republics such as India, have a combined head of state and head of government but the President remains responsible to the lower house of parliament; it elects the President at the beginning of a new Parliament, or when there is a vacancy in the office, or when the sitting President is defeated on a vote of confidence. If the Parliament cannot elect a new President within a short period of time (a week to a month) the lower house is dissolved and new elections are called.

Rhodesia between 1965 and 1979, and Zimbabwe between 1980 and 1987. The 1987 constitution abolished the Westminster system.

Nigeria following the end of British colonial rule in 1960, which resulted in the appointment of a Governor-General and then a President, Nnamdi Azikiwe. The system ended with the military coup of 1966.

Ceylon between 1948 and 1972, and Sri Lanka from 1972 until 1978 when the constitution was remodelled into an Executive presidential system.

Burma following independence in 1948 until the 1962 military coup d'état.